IN CONVERSATION

Shiraz Minwalla

forces and were formulated a hundred possible relevance to experiments and, as years ago. Mathematically, both these pointed out by Son and Surowka, also to equations are partial differential equa- something that must appear in quantum tions, which a priori have nothing to do field theories with certain anomalous with each other. However, there were structures. So the fluid gravity corre- suggestions from theory, that these spondence taught us something new were related. The suggestions came from about a classical subject that most people the so-called AdS/CFT correspondence, thought was fully understood. which says that certain quantum field theories admit a classical description in Do you ever get worried that this may be terms of equations of gravity, at a certain the most important scientific contribution limit (Figure 1). Also, the equations of of your life? hydrodynamics are believed to apply to Shiraz Minwalla all quantum field theories at appropriate (Laughs) Yes. To be honest I do worry

mathematical regimes. We pointed out about that sometimes. Shiraz Naval Minwalla is a theoretical that these three things making a triangle physicist at the Tata Institute of Funda- imply that, in appropriate regimes, equa- What is your current research interest? mental Research, . He is noted tions of gravity should describe hydro- for his pioneering work on dynamics. If this is true, then it should Right now, I am working in two different and quantum field theory. In November also be seen mathematically. That’s what areas. 2013, he was awarded the we did; we showed that, at proper re- One, I am studying the dynamics of by the Infosys Science Foundation and gimes, solutions of gravity equations Chern–Simons theories in 2 + 1 dimen- also the New Horizons in Physics Prize have a one-to-one correspondence with sions. Ordinary gauge fields in the large by the Fundamental Physics Prize Foun- those of hydrodynamics. It is not only N limit, have a large number of degrees dation, for his path-breaking work on interesting because it connects two oth- of freedom, and are difficult to solve. establishing the connection between erwise unrelated but concrete mathemati- However when they are self-coupled in a equations of fluid dynamics and gravity. cal equations, but also because it adds to Chern–Simons theory, their effective The Infosys Prize Presentation ceremony our knowledge of hydrodynamics. Most degrees of freedom is 0; they show no was held on 8 February 2014 at Banga- of the modern study on hydrodynamics dynamics and are of no physical interest. lore, where he shared his experiences in was done by Landau and Lifshitz. They If the gauge fields in a Chern–Simons research in an interview. Following are wrote this beautiful book on Fluid Me- theory are coupled to a few matter fields, excerpts from the interview. chanics, where they have given a relati- they become physical and are effectively

vistic generaliation of the equations of solvable. It is interesting because it is Do you think that the fluid gravity corre- hydrodynamics. They did it in 1930s, tied to the rich class of theories we see in spondence is your most important scien- which has remained unchallenged since string theory. Also, there is a nice lesson tific discovery? then. However, when my students and I one learns from this. There is a conjec-

were working with the equations of rela- tured duality between Chern–Simon Yes. I think the fluid gravity correspon- tivistic charged hydrodynamics, we theories coupled to bosons and to fer- dence is the single most important dis- found a mismatch with their general mions; under a certain map of parame- covery by me. equation. It was a term that was missed ters, they have the same solutions. This

by Landau and Lifshitz. This term had is of the nature of non-supersymmetric At a non-technical level, is it possible to describe this work?

The fluid gravity correspondence pro- vides a well-defined connection between two most studied non-linear partial dif- ferential equations in history. The first is the relativistic generalization of the Navier–Stoke’s equation of hydrodynam- ics. The equations of hydrodynamics are being studied by scientists and engineers for more than 200 years and they are relevant to various phenomena in the world. The second equation refers to

Einstein’s equations of gravity, which govern the geometry of space and time. The AdS/CFT correspondence suggests that equations governing hydrodynamics are They apply ubiquitously to gravitational related to equations describing gravity.

662 CURRENT SCIENCE, VOL. 106, NO. 5, 10 MARCH 2014 IN CONVERSATION dualities, which we didn’t know much which I find satisfying, are in areas work through the internet. Does it affect about when they were discovered. When where no one was working before. For our research? I was growing up in the world of physics, instance, ten years ago, I wrote a paper I saw supersymmetric dualities coming with Marsano, Kyriakos, Papadodimas It definitely does. It is both good and up one after another, and I was led to be- and Raamsdonk on how to compute bad. It is good because very fast scien- lieve dualities are part of supersymmetric thermal partition functions in Yang Mills tific progress can be made. Once a dis- quantum field theories. However, now theories in S3  S1. No one worked on covery is made, there is an explosion of with the new non-supersymmetric duali- that before, but it became a part of an knowledge in that area. It is bad because ties, we have a new class of theories active field. So that was quite satisfying. it hurts the diversity of the ecosystem. which are as rich as the supersymmetric So, I think the answer to your question is However, communication through inter- ones. This means there may be a huge sometimes yes and sometimes no. net is not same as communication in per- number of dualities in quantum field son. If you are in Harvard or Princeton, theories, which we haven’t explored yet. Do you think quality theoretical physics your thinking may get influenced by the I think it is an important lesson to learn. research is done in our country? trends, and the people around you whom The second project I am working on is you admire. This is not the case if you a bit speculative. It has to do with Wald Yes, definitely. Let me restrict my ans- are in India; being far from that influ- entropy. We know that Bekenstein and wer to string theory. A lot of quality re- ence, you can make your own judgement. Hawking proposed a beautiful formula search has come from just one scientist, Even though it is important to participate for entropy in Einstein gra- , who is one of the greatest in scientific discussions, historically iso- vity. But, in string theory most dynamics physicists of our times. Even if you take lation has helped India creatively and is is governed by higher derivative correc- him away, good quality research is done more of a strength, than a weakness. tions to Einstein gravity. Now Wald en- in India. Fifteen years ago, it would be tropy, proposed by Robert Wald, is an fair to say that there were only two In history, we have seen many scientific analogue of the Bekenstein–Hawking groups in the country dominating in breakthroughs were made by people who formula, in higher derivative gravity. string theory research, those in TIFR and were young. Do you think age is a barrier You can think of these as the first law of HRI (Harish Chandra Research Institute). for making major scientific discoveries? thermodynamics in a black hole. How- Both these places continue to have very ever, the deeper elements of thermo- strong groups. But interestingly, string What you are saying is more true in dynamics come from the second law, that theory research in India has broadened. mathematics than in science. I recently says entropy always has to increase. Now there are many small groups in the read a book by (Godfrey) Hardy, which Hawking showed from the dynamics of country where very good work is done. said that no major discoveries in mathe- Einstein gravity, that the black hole These places include IISc, which I can’t matics were made by people beyond the entropy always increases. It is not yet say is small anymore, and ICTS, both in age of 45. However, in science, I believe known, if this is true for Wald entropy. It Bangalore. In Chennai, we have good it is less true. As you said, people like seemed possible to me, that this can be young groups at IIMSc, CMI and IIT. Einstein and Heisenberg were young answered from fluid gravity correspon- My student Sayantani Bhattacharya, who when they were most active; but there dence. Hawking showed that for an en- is an exceptional physicist, has recently were also people like Bohr, who were tropic current in a perfect fluid, there is joined IIT Kanpur. We also have good not so young. In the field of string theory an entropic current in Einstein gravity. I string theorists at IISER, Pune, IOP it is least true. Indeed as you grow older, have been discussing with my students (Bhubaneswar) and IIT Bombay; ... I you lose your quickness, and that cer- and collaborators whether it is possible may have missed a few places, which I tainly adds pressure. However, as you to address the problem of the second law don’t mean to be not good. What is im- grow older you also get to know more; of Wald entropy systematically, from the portant is the diversity around the coun- and knowledge always helps. In a com- lessons we learnt in fluid gravity. It is far try. People at different places develop plex theoretical field like string theory, from clear, if it is really possible. their own ways of thinking instead of where the body of knowledge is so vast, getting influenced by one another, and often a lot of progress comes from mak- Is your work of the sort, where a lot of this is very healthy for research. Good ing inter-connections; and it is impossi- people are thinking of the same problem? postdoctoral positions are available inside ble to make connections between things the country. Unlike most people twenty you don’t know about. We have people If you are in a field where a lot of people years ago, today we have many young like Ashoke Sen, Strominger, Vafa and are already working, it can be difficult to physicists who obtained their PhDs in- many others who were well over their do something really impressive. It may side India. Our research ecosystem is not forties when they were acknowledged as not be the same as in a field where no dependent on people outside the country the leaders of our field. In our field one is working. I think I have worked in anymore and I believe this autonomy is knowledge certainly helps. both kinds of fields. Before our work on something very positive. fluid gravity, a lot of people were work- How does theoretical physics affect soci- ing on linearized hydrodynamics, linea- In the past most major scientific discov- ety? rized response functions, etc. Although eries were made by physicists thinking we worked from a different angle, I independently of what others were think- Looking at it from a broad perspective, would say it was already a very active ing around the world. But in the modern theoretical physics that was done hun- field. However some of my other studies, setting, we can easily access others’ dred years ago has had an enormous

CURRENT SCIENCE, VOL. 106, NO. 5, 10 MARCH 2014 663 IN CONVERSATION impact on our society today. For example, no excuse for the Indian society in this rule that says somebody must retire at a without quantum mechanics we wouldn’t regard. Every school in our country must certain age; because that is age discrimi- have superconductors; and without them give reasonable education to the stu- nation. They can continue their jobs as we wouldn’t have computers and much dents, so that it can bring out their abili- long as they keep doing their duties, like of the electronic industry. Practical life ties. We, the middle class, don’t take this teaching and research. It is certainly true would have been much different without seriously because our children go to rea- that as you grow old, you keep losing theoretical physics that was done hun- sonable schools. It is the middle class your quality and creativity in your re- dred years ago, although the concerned that makes the bureaucracy, and we must search. However, it is seen as a compen- physicists were not aware of these appli- treat this with the seriousness it deserves. sation; after all, people who become cations. Even today research in theoreti- If we approach it with seriousness, I am professors, often have what it takes for cal condensed matter physics has a lot sure it can be done. jobs with five or ten times more money of potential applications. Theoretical than what they get. They sacrifice that physics of the kind that I do, seems How difficult is it to get a proper job for luxury, for serving science, and in return unlikely to have any application in the a graduate student in theoretical physics, get a good old-age. In India, this is not next fifty years. It is very hard to imag- specifically in high energy or string the- the case, and it can be hard on people. I ine technical applications of our work, ory? see that among my colleages at TIFR. say, on understanding quantum chromo- When they reach 62 and all of a sudden dynamics (QCD) better; for which we In India, there are plenty of jobs avail- they are out, they don’t know what to do. need to bring nuclei of two atoms to- able for someone who shows a certain On the other hand, we also need to make gether to see the strong interactions, passion for the subject and has the ability room for young people. ... I don’t have a which sounds unlikely to be realizable in to demonstrate. In TIFR, for instance, we very clear opinion on this. May be I will, a fifty year timescale. However, the theo- can hire more people than we do if we when I reach that age. retical work of our sort is a part of an find the right candidates. The same is ecosystem. The mathematical formula- true for the IISERs, IITs, and so on. Say a few words about youngsters who tions we do, lead to better understanding Availability of positions does not hold us wish to pursue a career in theoretical of other areas of physics, say condensed back, rather it is the other way round. physics matter. The impact may be limited, but it Positions exist, but they can only be is quite satisfying for us. filled by suitable candidates; those who Physics rewards different kinds of tal- display both passion and ability. If you ents. Intelligence is obviously rewarded, How can we motivate people with poor have these, apart from your accomplish- but less than you might think. A certain standards of living, towards theoretical ments, it is not difficult to get a job. A level of intuition, instinct or feel for the physics? Is the Indian Government career in physics or in science is not a truth is important. A certain level of con- spending enough on this field? routine job like, say, being a bank man- fidence, that does not tend to stupidity, ager. It takes more than attaining certain can be helpful. You may feel you are In India, the Government schemes are number of skills. You need to be crea- right about something and others may quite impressive for a student in theoreti- tive, have some spark and show your in- think you are being stupid. It is important cal physics. Apart from getting a reason- terest. Without them it can get difficult. to believe in yourself after weighing their able stipend in Ph D, one also gets words properly. A certain irreverence government fellowships, like INSPIRE. Should scientists ever retire? towards authority sometimes helps you However, the real problem in our country to be creative. If you feel you are strong is the primary education, which fails to This question has two elements to it. in some field, you can help by contribut- motivate people. Good education is the Should they keep holding formal posts at ing to that field. We have contributions best way to motivate students, towards the institutes? When do they stop doing from physicists who are very mathemati- physics, or other areas in science. or loving science? Most find it hard to cal in their work and also those who are Roughly, three-fourth of the country’s retire in the second sense. They can not. Both are great. Don’t get obsessed population gets so poor education that never stop loving science, or following about things you can’t. Follow your guts, they fail to make any contribution to any it; because science is a passionate profes- follow your instincts and do what’s fun. intelligent activity of the country. Pri- sion, where it really matters how much mary education in our country is dismal. you are enjoying it. But part of the ques- Apratim Kaviraj, Centre of High Other countries across the world, includ- tion is also about the jobs. Let’s see how Energy Physics, Indian Institute of Sci- ing those poorer than us, give better pri- it is answered in different societies. In ence, Bangalore 560 012, India. mary education to their children. There is the US, the legal system won’t allow a e-mail: [email protected]

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